Process for the recovery of ammonia



Feb. as, 1949-.

J- W. TETER ET AL PROCESS FOR THE RECOVERY OF AMMONIA s sheps-shee't 2 Filed Deo. 29,V 1942 of @f .y

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PROCESS FOR THE-RECOVERY OF AMMONIA Jah/N /4/. 727522 BY FoERT/v. Sica/(EY A TT ORNE Y' Patented Feb. 8, 1949 PROCESS FOR. THE RECOVERY OF AMNIONVIA John W. Toter, Chicago, Ill., and Robert H. .Stookey, Whiting, Ind., assgfnors to Sinclair Refining Company, New York, N. Y., a corporation of Maine ,Application December 29, 1942., serial No. 470,450

This invention relates to the separation and recovery of ammonia and hydrocarbons from mixtures containing these constitutents. The invention is particularly applicable to the separation and recovery of unreacted ammonia and of hydrocarbons contained in the effluent gases from a process in which olenes are aminated by reaction with ammonia.

In amination processes of the type mentioned,

an oleiine such as propylene, for example,

and ammonia, advantageously anhydrous, are brought into intimate contact with a suitable catalyst at an elevated temperature and at superatmospheric pressure with resulting production of organic nitrogen-containing material comprising the aminated olene. The amination reaction usually effects only a partial conversion of the oleiine with the result that the eiiluent from the process contains important proportions of unreacted olene and ammonia. Although the un-- tion results in an important alteration of the relative proportions of propylene and ammonia in the eiiluent as compared to the relative proportions of propylene and ammonia initially charged to the reaction zone.

The desired reaction product may be recovered advantageously by passing the composite eluent from the reaction zone to a stabilizer maintained under pressure and wherein the organic nitrogencontaining product, i. e., the aminated olene, is separated by controlled volatilization of unconsumed reactants and products of the side reactions. The aminated oleflne is ywithdrawn from the lower part of the stabilizer, and the more volatile unreacted oleiine and ammonia and products of the side reactions -pass oil as overhead. The volatile overhead products are advantageously at least partially condensed to provide a reflux material for the stabilizer, and the portion of the overhead not returned for refluxing contains, as noted hereinabove, not only the products of the side reactions from the'amlna- 1.01am. (ci. 26o-585) 2 e tion reaction zone but also the'unreacted. olene and ammonia. Y

A process has been proposed for the separation and recovery of ammonia from this stabilizer overhead involving total absorption and recovery of the ammonia by a combined aqueous absorption and distillation system. The relatively large amount of unreacted ammonia in the stabilizer overhead'i.y -e.,'the amination reaction eiiluent from which the amination product has been removed, requires an absorption-distillation syst-em of large capacity. Moreover, the use of an aqueous absorption medium `requires careful' control ofthe distillation step in order to obtain substantially anhydrous ammonia which is usually methane, ethane, etc., which are not condensed or absorbed in the liquid hydrocarbonlayer, remain in the vapor phase and may thus readily be separated from the liquid components. The upperV layer comprises the hydrocarbons containing a small proportion of the ammonia, and the lower layer comprises the ammonia containing a small proportion of the hydrocarbons. In accordance with our invention, We cool the mixture of yammonia and hydrocarbons to a temperature of 74 F; or below under suicient pressure to establish substantially liquid phase conditions at that temperature, and effect settling .of the cooled liquid mixture with resulting formation of ktwo distinct layers comprising lthe ammonia and the hydrocarbons, respectively. We then separate the ammonia and hydrocarbon layers. Settling ofthe liquid mixture is advantageously carried out in a suitable chamber from the upper vapor space of which'the uncondensed hydrogen, methane, etc., may be withdrawn, and the ammonia and hydrocarbon liquid layers may readily be separated by decantation or the like. The greater part of the ammonia from the stabilizer overhead, and containing only a relativelyv small amount of the propane and propylene, is thus separately recovered for recycling to the reaction zone of the amination process. The remainder of the ammonia from the stabilizer overhead, contained in the propane-propylene liquid layer, is readily recovered by aqueous absorption followed by distillation in an appropriate absorption-distillation system of modest size.

We have found, furthermore, that the amine.- tion product is soluble in both the ammonia layer and the hydrocarbon layer. For this reason the amination product is removed in accordance with; our invention from the amination reactor eiiluent before separation of the ammonia and hydrocar bon components rather than to remove the amination product from these components individually after their separation from one another;

In cooling the mixture of ammonia and hydrocarbons obtained as the overhead from the Vstabilizing operation of an amination process, advantage is taken of the cooling of this mixture effected in condensing the mixture for the return of a portion of the mixture as reiiuxing medium for the stabilizer. Partial cooling to the desired extent required in accordance with our invention is thus already provided by the usual operation of the aminationprocess.

' Cooling is carried out, in accordance with the invention, to such. an extent as to lower the temperature of the ammonia-hydrocarbon mixture to about 14 F. or below. We have found that under suicient pressure' to establish liquid phase conditions visible separation of the ammonia and the hydrocarbon component begins as the mixture is. cooled to a temperature oi about 74 F. The liquidv ammonia settles to the bottom and the liquid hydrocarbons float thereon in an upper layer; Although eective and useful separation occurs at this temperature, the ammonia is nevertheless. present in the hydrocarbon liquid layer in considerable concentration and the hydrocarbons are also present in substantial amounts in the ammonia layer- We have found, however, that at temperatures substantially within the range of :about 20F F; to -20 F. the separation so effected lis of such nature that the ammonia layer Ymay be returned directly, and without further treatment, to the amination reaction zone. Thus, for example, when a mixture comprising aboutv 40% .ammonia and 60% of a hydrocarbon component composed` oi about 34% propylene and about 56% propane is cooled to a temperature within the range of abouty 20 F. to 20 F., the ammonia layer contains only about 2% by Weight of the hydrocarbons. Moreover, the hydrocarbon layer contains only about 2% by weight of ammonia Within this temperature range.`

The eiect of the temperature to which the ammonia-hydrocarbon mixture is cooled upon the. sharpness of separation is illustrated in the table wherein there is presented experimental Vdata obtained by treatment of a mixture kof ammonia and hydrocarbons in which the hydro- .carbon component comprised 05% ethylene, 4.8% zethane, 33.3%. propylene 56.4% propane and .5.1% oil Cehydrocarbons, the percentages being by weight.. In each of the tests this hydrocarbon component andanhydrous ammonia were charged vin admixture to a calibrated Penberthy gauge oi about 150 cc. capacity in the ratio of about 60 liquid percent hydrocarbons to 40 liquid percent ammonia. rIhis ratio corresponds to a particularly advantageous feed ratio for an amination process for the amination of propylene. In each test the ammonia-hydrocarbon mixture was ycharged. to the gauge in such amount as to leave a vapor space of about 25 cc. at room temperature,

tained atY the specified temperatures and was allowed to stan-d` in the bath for 1% to 2 hours in order to insure that the temperature within the gauge Was the same as the temperature of the bath. .The gauge was then removed from the bath and the layers' were discharged into pressure-receivers. The liquid layers separately co1- .lected Vin the pressure receivers Were released through acid of known strength, and the acidinsoluble gas was collected, measured and analyzed. Titration of the acid indicated the amount of ammonia present in each layer passed through the acid.

Table Temperature, F' S0 74 70 60 30 30 20 0 -20 Pressure, #im in i280 260 255 210 140 ist v95 75 40 Vohper cent:

Upperlayer T0. 3 69. 2 63. 6 60.2 00. 6 57. 9 60. 0 57. 8 Lower layer....- 29. 7 30.8 36. 4 30. 8 39. 4 42.1 40.0 42. 1

ieiglit per cent: Upper 1ayer.. 66.0 64.0 59.0 55. 6 50. 2 53. 4 55 1 53. 3 Lower'laycri 34.0 35,'1 41.0 44. 4 43. 8 46. 6 44 9 46. 7

Upper layer:

Wt. percent N H3. 1 3.2 5. 5 Wt. per cmi; Olenc.. l 31.7 31,4 Wt. per cent Paraiiiu. 65. l 63.1 Lowerlayer:` 1

Wt. per ccnt NHL,-.. 89. 5 95. 7 90.2 98.0 97. 2 97. 4 Wi. per com oleane-. 5. 1 f 2; 1i 4. s o. s 1. 9 1.o vWhpel cent Pnmfn. 5. 4 2.2i 5.0 1.1 0.9 1.6

The table shows that at 80 F. there is no separationbut. that at '74 F. there is a separation of' the'liqni'd ammonia-hydrocarbon mixture into layers. 'Relatively sharp separation takes' place at. about F. Optimum separation, as indicated Aby the relative concentration of one component in the layer of the other component, is obtained attemperatures substantially'w-ithin the range of. about 20 F. Vand 20 F. Within this latter Vrange the Vammonia layer .contains only about 2-3'% of the hydrocarbon component and the. hydrocarbon layer contains a minimum of the ammonia. At higher temperatures, however, each layer contains more of the other component and the solubility of ammonia in the hydrocarbon layer is apprf-:ciablyy greater than the solubility of the hydrocarbonsY in the ammonia layer. At 60 F.,ffo1 example, the hydrocarbon layer contains 21.4 weight percent ammonia, whereas the ainmonia layer contains only 10.5 Weight percent of the hydrocarbons.

The chartA comprising Fig. l shows the ammonia, olen'e, and parain separation in the top Vlayer Vwithin the temperature range .of 60 F. to -20'F.,. and the chart reproduced as Fig. 2 shows the ammoniasand hydrocarbon separation in the .bottom layer within this temperature range. Fig.

3 lillustrates the ammonia distribution between the two layers within the same temperature range. These charts show that with4 the ammonia-hydrocarbon mixture described above, separa-tion of the ammonia from the propane-propylene hydrocarbon component occurs to a substantial extent even at temperatures of about 60 F. and that particularly advantageous separation takes place wiiir the temperature range of. about 20 F. `to

It should be noted, however, that the advantage in cooling the ammonia-hydrocarbon mixture to a temperature within the range of about 20 F. to 20 F. is not merely one of degree. The olene (essentially propylene) appears to be selectively dissolved in the ammonia layer Within the range of temperatures tested. For example, analysis of the propane-propylene mixture described hereinbefore in an Orsa-t apparatus showed that the mixture contained about 34.0 weight per cent propylene. At 20 F., 0 F. and 20 F., the weight per cent of propylene in the hydrocarbons of the hydrocarbon layer, as determined by the Orsat apparatus, is substantially the same as in the original propanepropylene component of the ammonia-hydrocarbon mixture charged. However, at 20 F., the olene comprises 45.0 weight per cent of the hydrocarbons contained in the ammonia layer, at 0 F.it comprises 67.8 weight per cent of the hy- A(irocarbons, and at 20 F. it comprises 37.0

weight per cent of the hydrocarbons in the ammonia. These relative concentrations of the oleflne in the hydrocarbons in the upper and lower layers are graphically illustrated in Fig. 4. It is clearly shown therein that Iwithin the temperature range of about 20 F. to 20 F. the olefine isselectively concentrated in the hydrocarbon component of the ammonia layer, this concentration reaching a maximum at about 0 F. This :concentration of olene in the hydrocarbon component of the ammonia layer is particularly important when the ammonia layer contains a substantial amount of hydrocarbons, as is the case, for example, where the hydrocarbon component of an ammonia-hydrocarbon mixture contains 'relatively large amounts of propylene.

As indicated above, the olene content of the hydrocarbon component of the ammonia-hydrocarbon mixture has a pronounced effect on the separation of the two layers. For example, in the case of a hydrocarbon component comprising 76.0 weight per cent propylene and about 22 weight per cent propane, an admixture of 84 cc. of this hydrocarbon with 56 cc. of anhydrous ammonia, cooled to a temperature of F. under a pressure of 96 pounds per square inch and settled and analyzed as in the preceding examples, the relatively high content of olene in the hydrocarbon component caused 19.5 weight per cent of the ammonia to appear in the upper (hydrocarbon) layer and 11.0 weight per cent of the hydrocarbons to appear in the lower (ammonia) layer at this temperature. Moreover, although the olene (propylene) content of hydrocarbons in the upper (hydrocarbon) layer was 75.0 weight per cent and thus substantially the same as in the original hydrocarbon component charged, the olene content of the hydrocarbons in the ammonia layer had increased to 82.5 weight per cent. Thus, an increasing propylene content in the hydrocarbon component of the ammoniahydrocarbon mixture increases the mutual solubility of the hydrocarbon and ammonia components in one another at a specific cooling temperature. Temperatures below about 0 F., and advantageously of about F., sharpen the degree of separation between ammonia and such hydrocarbon components of high olene content at some sacrifice in the concentration of the propylene in the ammonia layer.

Accordingly, cooling of an ammonia-propylene containing hydrocarbon mixture to a temperature within the range of about 20 F. to 20 F. effects not only separation of the ammonia and hydrocarbon components but effects concentration of the propylene v:in the hydrocarbons absorbed in the ammonia layer, maximum concentration taking place at about 0 F. As a result of this concentration,v the ammonia layer is preeminently suitable for direct return to the reaction zone of a propylene amination process. Within this temperature range, maximum separation of the ammonia and hydrocarbon components of the mixture thereof is ef- `fected by cooling to a temperature of about 20 F.l Accordingly, the return with the ammonia of propane, which is undesirable in the amination reaction zone, is suitably controlled within our preferred temperature range. By cooling to a temperature of about 0 F. the amount of propane in the hydrocarbons contained in the ammonia is kept low by the selective concentration of propylene in these hydrocarbons. By cooling to a temperature'of about 20 F., the total amount of hydrocarbons, and hence of propane, contained in the liquid ammonia is reduced to a minimum.

Further tests carried out with such a 76% propylene hydrocarbon component, to which a substantial amount of a butane-butylene fraction had been added, showed that the C4 hydrocarbons are selectively concentrated in the upper (hydrocarbon) layer. Thus, in such a composite .hydrocarbon mixture containing 26.9 weight per cent C4 hydrocarbons and mixed Withanhydrous ammonia in the ratio of about 65 parts of the hydrocarbons to 75 parts of ammonia, the amount of C4 hydrocarbons in the hydrocarbons contained in the ammonia layer upon separation at a temperature of 15 F. ranged from 0.4

the ammonia layer and an undesirable concentration of butane (or of C4 hydrocarbons) is not built up in the amination reaction zone. the separation of ammonia in accordance with our invention makes possible the direct return of the ammonia to the propylene amination reaction zone Without any detrimental effect on the desired maintenance of a low concentration of C4 hydrocarbons in the reaction zone.

The pressure required for carryingA out the method of our invention is essentially that required to establish substantially liquid phase conditions and may readily be ascertained for each particular ammonia-hydrocarbon mixture at any desired cooling temperature. The long settling period described in connection with the foregoing tests is not necessary in the practice of our invention inasmuch as visible separati-on of the cooled liquid mixture into separate layers takes place immediately upon cooling of the mixture of ammonia and propane-:propylene to temperatures of about 74 F. and lower. Thus, separation of the two layers may be eected readily and emciently by separately and continuously withdrawing the layers from a decanter or settling vessel to which the cooled mixture is continuously charged under appropriate pressure to maintain substantially liquid phase conditions.

A specific embodiment of our invention in an amination -processis illustrated in Fig. 5. An

Thus,

olenehydrocarbon, consisting predominantly of :propylena and substantially anhydrous ammonia ,are charged to a reactor in which they are brought into contact with an aminaton catalyst atan elevated temperatiue and pressure. The

`eiiluent from the reactor is delivered to the stabilizer provided with a heating kettle and Aadapted to eect volatilization of the unreacted ammonia and propylene and of products of side reactions, such as hydrogen, methane, ethane,

ethylene, propane, etc., in the form of overhead with accumulation of the amination product in the bottom of the stabilizer from which it is removed. The overhead is cooled and condensed byrefrigeration, say by a liquid ammonia cooling coil, iand the condensed overhead is allowed to settle in the decanter with the formation of two liquid layers. A portion of the condensed overhead Vmay be returned advantageously to the Y.stabilizer as a reux -mr-zdiurn.` The upper layer, comprising the liquid hydrocarbons, is withdrawn Vfrom the decanter for recovery and treatment to provide propylene for recycling to the reactor. ,The relatively small amount vof ammonia contained in the upperlayer maybe separated from the hydrocarbons-by any appropriate procedure,

.advantageously by aqueous absorption anddistilstabilizing the resulting mixture to recover the aminated propylene and to yproduce a gaseous mixture of the unreacted components consisting predominantly of ammonia, :propane and propylene, coolingthe gaseous mixture to a temperature of about 0 F. under sufficient pressure to establisli substantially liquid phase conditions at such temperature, eiecting settling of the cooled liquid mixture Witn resulting formation of two distinct layers one of which comprises predominantly the ammonia and the other comprises predominantly the propane and propylene, separating the layer comprising predominantly the animen-ia and the layer comprising predomi- `nantiy the propane and propylene and returning the ammonia to the amination operation.

JOI-IN W. TETER.

ROBERT H. STOOKEY.

REFERENCES CITED The following references are of record inthe iile of this patent:

UNITED STATES PATENTS v Date 

